A susceptibility locus for schizophrenia in the 'pseudo-autosomal' region has been proposed on the basis of the reported excess of sex-chromosome aneuploidies (e.g. XXY and XXX) among patients with schizophrenia and the finding that schizophrenic sib-pairs are more often of the same than of the opposite sex. This hypothesis has been tested in 83 sibships with two or more siblings fulfilling Research Diagnostic Criteria for schizophrenia or schizoaffective disorder. Alleles at the pseudo-autosomal telomeric locus DXYS14, which is unlinked with sex, were analysed using the method of affected sib-pairs. Affected sibs shared alleles at DXYS14 more frequently than expected by random Mendelian assortment, supporting genetic linkage between DXYS14 and schizophrenia.